Bone Markings of the Radius.
a. Radial Head (caput radii) is a proximal, disc-shaped prominence. Its concave superior surface articulates with the capitulum of the humerus and its cylindrical lateral surface articulates with the radial notch of the ulna.
b. Radial tuberosity (tuberositas radii) is an oval elevation on the proximal, medioanterior margin of the radius. It is an attachment point for biceps brachii muscle.
c. Radial Neck (collum radii) is the region of bone between the head and tuberosity.
d. Radial Shaft or body (corpus radii) is the elongated region of bone that extends distal to the tuberosity.
e. Interosseous border of the radius (margo interosseus radii) is the medial edge (margin) of the bone where the interosseous membrane attaches.
This thin connective tissue membrane divides the forearm into anterior and posterior compartments. It also is an attachment point for several forearm muscles and transfers tension from the radius to the ulna.
f. Styloid process of the radius (processus styloideus radii) is a thick, pointed, lateral projection from the distal end of bone. It forms the lateral portion of the wrist joint and serves as an attachment site for the brachioradialis muscle and radial (lateral) collateral ligament.
g. Ulnar notch (incisura ulnaris) is a mediodistal concavity that allows the radius to pivot around the head of the ulna during pronation and supination of the forearm, wrist, and hand.
Bone Markings of the Ulna.
h. Olecranon or olecranon process (olecranon ulnae) is a large, fan-shaped superior projection from the proximal end of the ulna. Its curved anterior surface forms the superior portion of the trochlear notch (see below) and its rounded posterior surface forms the bump of the elbow. It also is an attachment site for the triceps brachii, anconeus, and flexor carpi ulnaris muslces.
i. Coronoid process (processus coronoideus) is a triangular-shaped, anterior projection from the proximal end of the shaft. It is an attachment site for the brachialis muscle.
j. Trochlear notch or semilunar notch (incisura trochlearis) is a deep depression at proximal end of the ulna formed by the curvatures of the olecranon and coronoid processes. This area articulates with the trochlea of the humerus at the elbow.
k. Radial notch (incisura radialis) is a depression along the lateral edge of the coronoid process that articulates with the head of the radius. The joint allows the radial head to rotate against the proximal end of the ulna during pronation and supination.
l. Ulnar tuberosity (tuberositas ulnae) is a roughened eminence located just inferior to the anterior tip of the coronoid process. This area serves as the distal attachment (insertion) point for the brachialis muscle.
m. Ulnar shaft (corpus ulnae) is the body of the bone that extends distal to the ulnar tuberosity.
n. Interosseous border of the ulna (margo interosseus ulnae) is the portion of the lateral margin of the bone where the interosseous membrane attaches.
o. Ulnar head (caput ulnae) is a small, rounded eminence at the distal end of the ulna. Its inferior surface articulates with the with articular disc cartilage of the wrist, and its lateral surface articulates with the ulnar notch of the radius during pronation and supination of forearm, wrist, and hand.
p. Styloid process of the ulna (processeus styloideus ulnae) is a small projection that descends from the posterior portion of the ulnar head. It is an attachment point for the ulnar collateral ligament, which connects the ulna to the triquetral and pisiform carpal bones at the wrist.